Automotive fuse boxes are the central point through which wiring passes to all the electrical equipment. The fuse box is an essential part in a vehicle because if anything electrical goes wrong, the in-line wired fuse blows. If you install new electrical equipment into your vehicle, such as a car stereo, you need to add wiring to the fuse box. Most vehicle fuse boxes have several extra fuses so you can add other equipment easily.
Open the fuse box cover. Find the fuse layout diagram that's either on the outside of the fuse box cover, or on the inside. It details what each fuse connects to, and tells you which fuses are not in use.
Select a spare fuse connection. Look at the connection and you can see "in" and "out" labelled, though the wording may be slightly different. The "in" marking indicates it's from the battery. The "out" means it goes to the electrical equipment.
Locate the red (positive) wire from the electrical equipment and connect the end to the "out" terminal on the spare fuse. Remove the fuse using your fingers and slide the wire into the connector. It clips in place.
Attach another red wire to the "in" terminal on the fuse using the same method. The opposite end of the wire connects to the battery. Check the amperes for the electrical equipment on its label. It's important the fuse matches the equipment's amperes. Place the correct amperes fuse into the fuse holder. Push it into place using your fingers.
Replace the fuse box cover. Check that your electrical equipment operates now that you've added the wire to the fuse box.